PoC service is a trunking media communication service based on the Internet Protocol, IP. The service is implemented through the bearer network with the adoption of half-duplex Voice over IP, VoIP. After the user list of a group is set, one PoC user can set up peer-to-peer or peer-to-multipeer half-duplex conversations with other PoC users.
Specific entity relations in a PoC network is shown in FIG. 1, wherein a Controlling PoC Function, CPF, is the communication core, which carries out control in a centralized way to perform session control, communication control such as establishing/canceling sessions, signaling and media negotiation, processing requests, and allocating media streams, group policies, collecting and controlling Quality of Service, QoS, parameters, and user plane adaptation.
Each client corresponds to a Participating PoC Function, PPF. All PPFs send requests to the CPF, and the CPF coordinates and controls the session processes (such as media allocation, data transfer, and authority and role transition).
Clients that join a session communicate with each other by sending requests to and receiving instructions from the CPF via PPFs. The CPF allocates media and data to PPFs according to related policies. Then PPFs forward the media and data to their corresponding clients. Thus, point-to-point and point-to-multipoint communications between clients are implemented.
CPF and PPF are functional modules. CPF and PPF may exist in one PoC server or in different PoC servers and execute different functions.
A client is the functional entity of a PoC user that joins a session. Multiple PoC users can form a PoC group.
To cater to the ongoing development of PoC application technologies, the Open Mobile Alliance, OMA, defines the PoC 2.0 specifications. Relative to PoC 1.0, the biggest change in PoC 2.0 is that PoC 2.0 supports group multimedia sessions. In addition, an entity called PoC Box is added into the PoC structure, with an intent to provide user storage space on the network side or the PoC terminal side.
According to the technology of PoC user storage space, a PoC user may have a storage space in the network, NW or the user equipment, UE to store contents including sessions and media streams, e.g. audio, video and data. The user may set a certain specific condition so as to store sessions/media that cannot be received in time into the PoC user storage space, known as a PoC Box, of the UE or NW, and the PoC Box may be set in the network party or a mobile telephone, for processing in idle time; or the user may switch between PoC client and PoC Box dynamically during a PoC session.
When the condition set by the PoC user is met, a PoC session may be stored into the storage space of the PoC Box. According to where the PoC Box is located, a PoC Box may be an NW PoC Box or a UE PoC Box.
With the addition of the feature, a new charging technology is challenged for a PoC system. In the conventional technology, a method for charging includes the following steps.
1. A number of PoC users participate in a PoC group session via a controlling PoC server;
2. The controlling PoC server receives a request, inviting a PoC Box to join the group session;
3. The controlling PoC server executes a PoC group control policy and obtains charging information of PoC group session participants according to the mode by which a normal PoC client joins a PoC group session;
4. The controlling PoC server sends the obtained charging information to the charging system; and
5. The charging system performs charging according to the charging information.
In the foregoing layout, the controlling PoC server looks the PoC Box as a normal PoC client. This is said in the charging information sent by the controlling PoC server to the charging system, the info corresponding to a PoC client and that to a PoC Box are same. However, to provide better quality service for users, it may be necessary to design a charging scheme specially for the PoC Box. The foregoing scheme performs charging according to only the number of participants and therefore accurate charging is impossible.